St. John's Wort May Interfere With Drug Effectiveness

February 16, 2000

2 Min Read
St. John's Wort May Interfere With Drug Effectiveness

LONDON--St. John's wort, known to relieve mild depression, may interfere with drugs used to treat HIV infected people and heart transplant patients. Popular in Germany, some U.S. physicians had begun recommending it to patients and were reporting that the herb had been effective in stemming depression. However, two new studies published in The Lancet<$> medical journal found St. John's wort dulled the effectiveness of both the transplant drug cyclosporin and the HIV medicine indinavir.

In one study, a decreased level of cyclosporin caused two heart transplant patients taking St. John's wort to begin to reject their transplanted hearts. Withdrawal of St. John's wort allowed the drug to do its job; no further episodes of rejection occurred. In another study, St. John's wort caused the blood concentration of indinavir to decline 81 percent in eight AIDS patients. A low level of indinavir in an AIDS patient's body is a common cause of resistance and treatment failure. Although few participants were used in these studies, some supplement researchers say the methods and results render these findings significant.

The studies suggest St. John's wort may influence an important metabolic pathway, according to an FDA advisory. Researchers believe St. John's wort makes drugs move through the body more quickly than normal, hindering their effectiveness. Approximately 50 drugs are circulated through the body in the same manner as indinavir and organ-rejection drugs--including cholesterol-lowering drugs and oral contraceptives.

"It means that St. John's wort ought to be regulated," said David Flockhart, associate professor of medicine and pharmacology at Georgetown University. "And a lot of people aren't going to like me for saying that, but you've got an herbal here that has a major drug interaction." FDA reported it was working with drug manufacturers to ensure that medication labels are revised "to highlight the potential for drug interactions with St. John's wort." Sales for St. John's wort in 1999 were estimated at more than $200 million.

Still, scientists point out that the safety and efficacy of St. John's wort have been proven in numerous U.K. studies. In fact, its effects on the metabolic pathways are the same as those caused by certain foods and drinks, including grapefruit juice, broccoli, Brussels sprouts, charcoal-grilled red meats and red wine. In addition, ethanol and cigarette smoke produce similar effects.

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